1. Field of the Invention
The present invention generally relates to an internal combustion engine. More specifically, the present invention relates to a structure of an internal combustion engine that aides in lubricating sliding portions of the engine.
2. Background Information
Engines have many moving parts that operate at high speeds. The sliding portions of these moving parts are subjected to friction and can therefore wear away. In view of this situation, lubricating oil is often supplied to the sliding portions by a pump driven by the engine. Some vehicles have an electric mode in which the engine itself stops and the vehicle is propelled by an electric motor alone. In such hybrid vehicles, the engine sometimes operates very infrequently. In particular, the engine may at times operate very infrequently in plug-in vehicles capable of being supplied with electrical power from an outside power source. In such hybrid vehicles, the pump stops when the vehicle is propelled by the motor alone, and lubricating oil cannot therefore be supplied to the sliding portions of the engine. In other words, lubricating oil could fail to drip down or provide lubrication when the engine has been stopped for a long time.
In the engine described in Japanese Laid-Open Patent Publication No. 2005-90362, lubricating oil in an auxiliary tank is supplied to an oil pan such the oil level in the oil pan is raised to a height that reaches the crankshaft bearings when the engine is stopped. In this way, the crankshaft bearings are lubricated when the vehicle is propelled by the motor alone. Thus, with this arrangement, excessive wear of the engine crankshaft bearings can be effectively prevented. The lubricating oil is then returned to the auxiliary tank during engine operation such that the lubricating oil level is thereby reduced so that the lubricating oil is not in contact with the crankshaft during engine operation.